Pregnancy-specific protein B (PSPB) and progesterone concentrations were determined by RIAs in venous plasma during early pregnancy after 177 artificial inseminations (AI) performed in 76 cows and 71 heifers. The females were bled at 24, 26, 30-35 days and approximately 70 days (for non-returns to oestrus) after AI. In non-pregnant females without extended CL maintenance (progesterone less than 1.5 ng/ml on Day 24) and or showing a normal time of return to oestrus (Group 1, N = 63), PSPB concentrations were undetectable whatever the stage after AI except in 2 cows. In pregnant animals (N = 83; Group 2) progesterone concentrations were greater than 10 ng/ml from Day 24 to the time of rectal palpation and PSPB concentrations rose continuously from 0.42 +/- 0.07 (s.e.m.) ng/ml (Day 24) to 4.06 +/- 0.3 ng/ml (time of rectal palpation). No coefficient of correlation between PSPB and progesterone concentrations was significant whatever the day of gestation studied. In cows with extended luteal function and subsequently found to be non-pregnant (late embryonic mortality) PSPB was undetectable (N = 21; Group 3) or detectable (N = 10; Group 4) at Days 24, 26 and/or 30-35 of pregnancy. At 24 and 26 days after AI progesterone concentrations were intermediate between those of Groups 1 and 2. At Day 24 females of Group 4 had higher progesterone concentrations than those of Group 3 (P less than 0.05), but no differences between these two groups existed at subsequent stages after AI.(ABSTRACT TRUNCATED AT 250 WORDS)